The present invention relates to the treatment of magnetic materials to increase the magnetic permeability of the magnetic material. In particular, the present invention is concerned with increasing magnetic permeability by subjecting a magnetic material to certain magnetic fields oriented in the direction of its hard axis of magnetization.
The present invention finds particular applicability for fabricated magnetic articles such as those used in thin film recording heads, magnetic shields, bubble memory (domain) devices, and magnetic sensing devices. Magnetic devices such as thin recording heads and bubble memory devices and some magnetic shields employ magnetically anisotropic films which are obtained by electroplating, and/or evaporation, and/or sputtering of the magnetic material under the influence of an orienting magnetic field to form a film. The resulting film exhibits magnetic anisotropy in the plane of the film. The direction along which the orienting field is applied during the deposition process becomes the longitudinal, preferred, or easy axis of magnetization, while the direction in the plane of the film orthogonal to the easy direction becomes the transverse or hard axis.
In magnetic devices such as those mentioned above, it is generally desirable to have as high magnetic permeability as possible. Such devices have two stable states of magnetization. In order to switch such a device from a first state to its other stable state, a field is applied in one direction, and when the applied field is released the device reverses back to its original state.
The reversal of a magnetically anisotropic film or device to its original state usually takes place by so-called rotational switching technique, as opposed to domain wall motion. Domain wall motion is about an order of magnitude slower than rotational and is usually accompanied by the undesirable Barkhausen noise.
Rotational switching technique makes use of a magnetic field applied in the transverse direction in conjunction with the magnetic field in the preferred direction to produce a torque action on the regions of magnetic domain thereby creating a decrease in the time required to reverse the film or device.
In many magnetic devices it is desired to have highly permeable materials, which in thin film form are capable of supporting a very large magnetic flux at relatively high frequencies such as those frequencies at which the film switches by rotation. Accordingly, the present invention makes it possible to usually substantially increase permeability through the whole range of frequencies of about 0.1 MHz to about 100 MHz.
The present invention makes it possible, in some instances, to more than double the permeability of the hard or traverse axis without often encountering hard axis locking of the film. Moreover, the present invention makes it possible to change the permeability of the hard axis of fabricated magnetic devices of intricate design such as present in thin film magnetic recording heads and laminated magnetic shielding structures.